An image display device such as a liquid crystal display or a projector is provided with a high pressure mercury lamp or the like as a light source. A high pressure mercury lamp is structured such that mercury or gas is confined in a glass tube. Thus, if the temperature of the lamp excessively rises, the glass tube will explode or quartz that composes the glass tube will deform and thereby its permeability will deteriorate. To prevent such situations, image display devices that use a high pressure mercury lamp as a light source are generally provided with a cooling fan that cools the light source.
Some of recent projectors that have a high pressure mercury lamp as a light source are provided with an energy saving mode that allows power supplied to the light source to be decreased to around several ten % of the maximum power (for example, around 50% to 90%). The energy saving mode might be set up for example by pressing a particular button mounted on the projector.
When power supplied to the light source is decreased, although an image that is displayed becomes dark, if the energy saving mode is set up in the following configuration, the image that is displayed can be sufficiently observed.
When an image projected by a projector is observed in the state in which a room lamp is turned on, since the room is bright, if power supplied to the light source is decreased, the image that is projected becomes less visible. By contrast, if the room lamp is turned off, since the room is dark, even if the amount of power supplied to the light source is decreased, brightness sufficient to see the image can be provided. Thus, if the room lamp is turned off, an image that is displayed can be satisfactorily observed even in the energy saving mode.
The smaller is the projection range (projection screen) on the projector the screen, the brighter the displayed image becomes. Thus, when the projection range is small, an image that is displayed can be sufficiently observed even in the energy saving mode.
Generally, the lower the power supplied to the light source, the lower is the temperature of the light source. Since power supplied to the light source in the energy saving mode is less than that in the regular mode in which the light source are lighted with maximum power, the rise of the temperature of the light source can be prevented.
Patent Literature 1 discloses a technique that considers the temperature changes of a light source that occur in the energy saving mode.
Patent Literature 1 discloses a projection type display device having a light source, a sirocco fan, and a duct that guides cooling air from the sirocco fan to the light source. In this projection type display device, when a power saving mode (corresponding to the foregoing energy saving mode) is set up, the amount of airflow supplied from the sirocco fan to the light source is decreased. As a result, the level of noise of the sirocco fan that operates in the power saving mode can be decreased.